For more than a decade now, Perth has been the beneficiary of all-too rare bipartisanship between the major political parties on water policy. That the politicians could have put to one side opportunism and short-termism is refreshing enough.

First week of winter saw big hits to water guzzlers

The West Australian

VideoFirst week of winter saw big hits to water guzzlers

That they somehow, whether by design or accident, managed to do such a thing on a matter as important as water supply is a blessing.

In order to explain, first think about the circumstances in which Perth finds itself from a water security perspective.

Rainfall in WA’s capital is down almost 20 per cent compared with its pre-1975 average.

Run-off into the city’s dams, which once provided practically all of Perth’s water needs, has fallen even more precipitously, as has recharge into its aquifers. The upshot is best exemplified by the average annual amount of water that flows into Perth’s dams. Whereas once they received more than 300 billion litres every year, the Water Corporation now relies on receiving no more than 25 billion litres a year.

But in 2015, not even that paltry figure arrived in the city’s reservoirs.

Instead, run-off was officially measured at 11.4 billion litres for the entire year — about three billion litres less than evaporated into the atmosphere. On average, Perth uses about 260 billion litres of drinking water a year, while the broader scheme including Mandurah, the Wheatbelt and the Goldfields consumes about 300 billion litres.

There were some visionary — some would say dumb-lucky — decisions to build water sources that were independent of what the weather delivered.

So far this year, virtually nothing has flowed into Perth’s dams as a dry autumn runs into a dry winter, with little rain on the horizon.

It has increasingly been this way for decades, with Perth seemingly in the grip of ever declining rainfall at the same time as average temperatures rise and demand for water from a growing population increases.

And yet Perth continues to be an oasis on the south western edge of the world’s driest inhabited continent, with per capita water use among the highest in the nation.

To be sure, Perth is lucky in the extreme to have an extensive and sizeable network of aquifers.

Dependence on groundwater has in many ways been the saviour of the city as the reliability of dams has slid steadily backwards for years.

But on top of this were some visionary — some would say dumb-lucky — decisions to build water sources that were independent of what the weather delivered.

The first mover was premier and water minister Geoff Gallop, who built Australia’s first full-scale desalination plant in Kwinana in the face of fierce criticism from the then Liberal opposition.

That plant delivered Perth an extra 45 billion litres a year.

Amid continually declining rainfall, Dr Gallop’s successor as premier, Alan Carpenter, pushed the button on another desalination plant at Binningup, north of Bunbury.

The plant had an initial capacity of 50 billion litres, but was designed to be doubled in size.

And so it was that in 2010, premier Colin Barnett finally put to bed his dreams of a Kimberley canal and went ahead with expanding Binningup.

In the meantime, a plan started by the Labor Party to boost Perth’s drinking supplies by pumping recycled sewage into the city’s aquifers was picked up and delivered by their Liberal-National successors.

This latest option is perhaps the most noteworthy of all, being a potentially controversial technology that could have been easily seized on by a gleeful opposition.

All up, the combined decisions of WA’s two most recent governments have delivered Perth an extra 178 billion litres of drinking water that will come out of people’s taps irrespective of whether it rains or not.